NCBC-373: .NET GetJSON operation throws System.ArgumentNullException

Change-Id: I9e822eb01a8d1783087e11e9ee135be95fdc4599
Reviewed-on: http://review.couchbase.org/33097
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>